The objective of this project is to define the maternal immunoregulatory cell interactions directed against specific embryonic or fetal antigens (EAs) that are expressed during the time course of pregnancy. Both the quality and quantity of the maternal anti-EA response present in various tissues during BALB/c mouse syngeneic pregnancy and postpartum will be investigated. The 86Rb microcytotoxicity assay in which residual, adherent target cells, having survived incubation with effector cells, are radioactively labeled will be employed to measure cytotoxic cell activity. The BALB/c tumor-cell lines, MCA 1315 and mKSA, will be utilized. The targets have previously been shown to express fetal antigens as is evidenced by the ability of effector cells from pregnant but not virgin animals to confer protection against tumor growth in an adoptive transfer assay. While we have preliminarily phenotyped the maternal anti-EA cytotoxic cell as a T-lymphocyte using monoclonal anti-Thy 1.2 plus complement depletion of cytotoxic activity, we will more fully define this cell by establishing its Lyt character. We will also determine if this cell is devoid of the asialo-GM1 marker in order to rule out the involvement of Thy 1.2-positive natural-cytotoxic cells. Additionally, we will examine whether the cytotoxic cell is MHC-restricted by using EA-positive BALB.B tumor targets. The presence of helper and suppressor-cell activity for cytotoxicity will be measured during culture generation of cytotoxic-effector cells from maternal tissue precursors. These regulatory cells will be characterized by the use of monoclonal antibody-directed, complement-mediated cytolysis and subsequent functional assays including experiments designed to demonstrate the kinetics of appearance. We will determine if suppressor cells inhibit the induction or effector phase of pregnancy-induced cytotoxicity and if suppressor cells act directly on the cytotoxic cell or inhibit helper-cell function. Requirementsfor suppressor T cell:macrophage (MO) interaction can be studied if depletion experiments impli-cate suppressor T cells. If MO involvement is apparent, alteration of the suppressive activity by indomethacin treatment will be attempted. Finally, if certain tissues in pregnant mice retain high cytotoxic-cell activity at times when other lymphoid tissues are suppressed, we will look at the role of contrasuppressor T cells in maintaining cytotoxic capacity. (AG)